As WLANs (Wireless Local Area Networks) continue to expand, the load of WLAN networks is also increasing. With the increase of the number of users, the efficiency of WLAN networks decreases sharply due to the dense networks. Simply increasing the transmission rate cannot solve this problem, multi-user parallel transmission as an alternative solution to network efficiency has aroused widespread concern and research.
In the related art, the multi-user parallel transmission technology includes Multi-User Multiple-Input Multiple-Output (MU-MIMO) technology, Orthogonal Frequency Division Multiple Access (OFDMA) Technology, among others. MU-MIMO utilizes space multiplexing technology to improve time and frequency utilization. The introduction of OFDMA technology enables multiple stations to be frequency-division-multiplexed over the entire bandwidth, making it possible to more efficiently utilize the result of inter-site frequency selection and improve spectrum utilization.
In a WLAN, multiple non-access point stations (non-AP STAs) send data to an access point (AP) at the same time, which is generally referred to as Uplink Multi-User (UL MU) transmission (a user is taken as a station). The AP sends data to multiple non-AP STAs at the same time, which is generally referred to as Downlink Multi-User (DL MU) transmission. A typical frame exchange sequence of UL MU and DL MU transmission is shown in FIG. 1.
The UL MU transmission requires to be triggered by an AP, for example, triggered by sending an independent trigger frame, or triggered by carrying a trigger information field in a radio frame. The trigger frame or the triggering information field includes scheduling information of the station, such as identification information of the station, time and frequency resource information used by the station for uplink transmission, and the like. After the AP sends the trigger frame or the trigger information field, the station receives the trigger frame or the trigger information field, and if its own identification information is carried therein, it indicates that the station is scheduled in this UL MU transmission, and if the station has data to be transmitted, the station transmits the data on the allocated time and frequency resource. In the following, a separate trigger frame or a radio frame carrying a trigger information field will be collectively referred to as a trigger frame.
In a WLAN, one AP and multiple non-AP STAs associated with the AP form a basic service set (BSS). In general, one AP can open a BSS, and the identifier BSSID of the BS is the Media Access Control (MAC) address of the AP. For the sake of application, a WLAN allows one AP to configure multiple BSSs. As shown in FIG. 2, the multiple BSSs and the BSS of BSSID which is the MAC address of the AP, make up a BSS set of the AP. Each BSS in the set may have respective service and security policy settings. Due to the small number of channels that are not overlapped in the non-licensed frequency band in Industrial Scientific Medical (ISM), if each AP sets up BSS independently, according to the principle that a channel for an AP does not overlap with a channel for another AP as possible it could be, since there is a small number of available channels, a larger co-channel and adjacent channel interference will be generated among the Aps. When one AP is allowed to configure multiple BSSs, this means that the same channel may be used by multiple BSSs, which can reduce interference. In addition, multiple BSSs in the BSS set have respective service and security policy settings, which can meet enterprise-level network requirements. For example, a BSS security policy used by a visitor may be set as Wired Equivalent Privacy (WEP), a BSS security policy used by internal employees is set to Wi-Fi Web Security Access 2 (WPA2, Wi-Fi Protected Access 2) and so on. The multiple BSSs actually correspond to a physical AP, and the AP broadcasts a parameter set of its own BSS set in a Beacon. For each BSS in the BSS set, a BSS parameter set includes a BSSID, an SSID, capability information of the BSS and so on.
In a multi-user parallel transmission scenario, an AP may trigger an uplink multi-user transmission at any station under its own BSS set. However, in this case, how to use trigger frames for uplink multi-user transmission and how to proceed the frame exchange sequence of the uplink multi-user transmission, these are technical problems to be solved.
This section provides background information related to the present invention which is not necessarily prior art.